Light emitting diodes (LEDs) are useful in various displays and especially in a new compact virtual display which utilizes an array of LEDs as an image source. The image source consists of a high pixel count (240 columns by 144 rows for a total of 34,560 pixels) 2-dimensional array of LEDs. The array of LEDs is used to form complete images containing pictorial (graphic) and/or alphanumeric characters. The complete images are then magnified to produce virtual images which appear to an operator to be at least the size of a standard sheet of paper.
In a copending application entitled "Electro-optic Integrated Circuit and Method of Fabrication", filed of even date herewith, and assigned to the same assignee, a method of fabricating LED arrays is disclosed utilizing mesa etched processing technology. A combination of wet and dry semiconductor etching is used for defining pixel emitting regions (anode isolation), accessing a highly conductive buried semiconductor layer for cathode contacting, and for isolating rows of pixels (cathode isolation).
One problem faced in productizing the etched mesa LED arrays, at the present time, is the nonplanarity of the resulting structures. Efficient opto-electronic light emitters require relatively thick layers of epitaxial material grown on a substrate. Because of the relatively thick layers of epitaxially grown material, the mesa etching produces nonplanarities which tend to be on the order of 1 micron or greater. Such large nonplanarities can lead to problems with resolute photolithography, uniform dielectric coverage, metal step coverage, or metal column and row connectors.
Accordingly, it is highly desirable to provide methods of fabricating LED arrays which overcome these problems.
It is a purpose of the present invention to provide a new and improved method of fabricating LED arrays.
It is a further purpose of the present invention to provide a new and improved LED array.
It is still a further purpose of the present invention to provide a new and improved method of fabricating LED arrays which is simpler and more efficient than prior methods and which is easily adaptable to high production levels.
It is another purpose of the present invention to provide a new and improved method of fabricating LED arrays which provides substantially planar semiconductor chips.